In many applications an enclosure or housing contains a primary liquid lubricant or sealing fluid. An example of a housing containing a primary liquid lubricant is an internal spur gear drive. An example of a housing containing a primary sealing fluid is the liquid seal for a clarifier or digester cover having a movable section, a fixed section, and a liquid seal assembly to prevent the free passage of gases from one side of the cover to the other. These housings are generally enclosed to exclude rain and contaminants, but they cannot be completely sealed against the ingress of humid air or the infiltration of liquid water, due to the nature of the movable components.
The introduction of liquid water arising from condensation of water vapor, or the ingress of liquid water, into liquid seal assemblies and liquid lubricant sumps has long been a problem. If the primary fluid, such as a sealing fluid or lubricant, has a specific gravity lower than that of water, the water displaces the primary fluid.
In a lubrication application, as would be found in internal spur gear drives, condensation and infiltrated water accumulating within reservoirs or sumps, displaces the primary fluid, which is usually a petroleum based lubricating oil, exposing bearing, gearing, and other surfaces to water, disrupting lubrication films and causing increased potential for corrosion. The accumulation of water in the drive housing can displace the primary fluid to the point of expulsion from the housing creating spillage.
In water and wastewater treatment plants, including municipal and industrial plants, the local relative humidity is increased by water vapor that is present above process basins, tanks, or vats. The housings of gear drives and liquid seal housings may be exposed to direct sunlight during part or all of the day or the housing may be exposed to other varying heat sources or cycles. As the housing is heated, the internal air within the housing is also heated and expands. The increased internal pressure expels a portion of the air from within the housing to outside of the housing. When the heating cycle ends, such as due to a change in a process or a shifting of sunlight away from the housing, the housing cools and the internal air contracts. The volumetric contraction of the cooler air lowers the internal pressure within the housing, drawing in ambient exterior air, which is sometimes laden with moisture. As this air cools within the housing, the dew point of the water vapor is reached and the vapor condenses forming beads of liquid condensate within the housing. The condensate is drawn by gravity to the low points within the housing, which in many cases is through the lubricant, where it accumulates below the lubricant, due to the specific gravity difference of the fluids. Water that has infiltrated the housing from the outside will also tend to accumulate below the lubricant or sealing fluid.
Within the housing, the condensate located below the lubricant does not evaporate as the heat input is generally less than the required latent heat of evaporation, and a lubricant such as oil, which has a lower specific gravity than water, forms a layer over the water condensate, thereby creating a vapor seal above the liquid water. Similar but more severe conditions exist when the housing is located within a cover that extends over a basin of liquid, such as water, wastewater or other process fluid, as the cover confines vapor in the vicinity of the drive housing.
A sewage treatment clarifier may be covered as an odor control measure. A liquid seal is employed in those cases where a portion of the cover must be free to move or rotate about the center of the basin. The seal is normally made up of an annular chamber having sides and a bottom. This chamber contains the primary fluid, usually petroleum oil or silicone oil. A cylindrical wall extends into the annular chamber and is partially submerged into the primary fluid. The cylindrical wall is connected to the movable cover section while the annular chamber is connected to another cover section, or the positions can be reversed. If the primary fluid is petroleum oil, the accumulation of water in the annular chamber can displace the petroleum oil to the point of oil spillage over the top of the chamber walls.
If the primary fluid has a specific gravity greater than water, as does silicone oil, the water remains above the primary fluid. Again, the water can accumulate to overflow the chamber walls. Before this, however, the water retained above the primary fluid can become a breeding place for flies, mosquitoes, and the like. A layer of petroleum oil can be poured over the silicone primary fluid to seal the water surface from the breeding insects, but again water can accumulate to overflow the chamber walls carrying the petroleum oil before it, leaving the water surface exposed.
Manual and continuous operating or automatic condensate systems have been developed to drain condensate and infiltrate from the housing. The manual system drains the condensate periodically by means of a manual valve or a motorized valve and switch arrangement. The continuous system drains the condensate as it appears or “automatically”.
Condensate removal systems previously used and as currently in use are generally V or U-shaped devices consisting of a collection leg and a discharge leg, and in some cases a transverse leg. A primary or first fluid, such as oil, and a secondary fluid, such as water, of different densities or specific gravities are contained within the V or U-shaped devices. The secondary fluid constitutes the liquid condensate, liquid infiltrate, or liquid condensate and liquid infiltrate combined, all hereinafter referred to collectively as “condensate”. Liquid water condensate has a specific gravity of approximately 1.00. Liquid water condensate collects in a sump within the housing and is drained into the collection leg of the removal system. The primary fluid, such as oil, is intentionally placed within the housing to act as a lubricant, as a sealing fluid, and/or as a corrosion inhibitor among other functions. The primary fluid, such as oil, usually has a specific gravity less than that of the secondary fluid or condensate, such as water. The elevation of the interface surface between the primary fluid and the secondary fluid is thereby established by setting the elevation at which the secondary fluid in the discharge leg of the removal system is allowed to discharge, and by the volume of the primary fluid in the housing which determines the elevation of the oil and water interface in the collection leg.
Condensate removal system designs attempt to adjust the discharge elevation of the discharge leg during initial installation to accommodate primary fluids with a narrow range of specific gravities. These designs, however, result in the fixing of the discharge elevation at the time of installation without provision for additional adjustment during the service life of the equipment.
If, in the case of a gear housing, a primary fluid, such as a lubricant, is used that is outside of this range of initial installation parameters, the system may not operate properly. This has been one of the causes of operational problems in preceding condensate removal systems. The condensate removal system may be rendered inoperable due to a replacement of the first fluid by a third fluid of a lower or higher density or specific gravity than that of the first fluid, which causes the elevation of the interface of the third fluid and the second fluid in the collection leg to move outside of the design range.
If the specific gravity of the third fluid is higher than that of the first fluid, the elevation of the interface between the third fluid and the second fluid in the collection system is lowered relative to the elevation of the interface of the first fluid and the second fluid. When the fluid interface between the second fluid and the third fluid reaches the level of the connection between the collection and discharge legs, the third fluid is no longer sequestered in the collection leg portion of the V or U-shaped device and will flow to the discharge leg, resulting in a loss of the third fluid, such as lubricating oil, from the housing reservoir. The addition of make-up third fluid to raise the third fluid free surface to design levels only forces more third fluid from the reservoir and collection leg, while potentially ejecting it from the discharge point.
During normal seasonal lubricant replacement, the primary fluid may be replaced with a third fluid of lesser density or specific gravity than that of the primary fluid. The elevation of the interface between the third fluid and the second fluid within the collection leg rises relative to the elevation of the interface of the first fluid and the second fluid. When the fluid interface reaches the level of critical surfaces, such as bearing races and rolling elements or gear teeth, lubrication breaks down and lubricant starvation results. Corrosion also accelerates under these conditions. Additionally, the free surface of the third fluid may be raised resulting in the lubricant being expelled from the housing through seals not normally exposed to the original primary fluid. These situations have not been addressed in the industry.
Another common cause of failure in continuous condensate removal systems that has not previously been addressed is the loss of liquid condensate from the collection leg due to evaporation of condensate from the discharge leg through the discharge port without adequate replacement of liquid condensate to the system by the accumulation of condensate within the housing reservoir. This may seem in conflict with the desired result, which is the removal of condensate from the system. However, the height of the column of condensate within the collection leg must be maintained at a relatively constant elevation. When condensate within the housing arrives at the collection leg an equivalent volume of condensate is discharged through the discharge port of the discharge leg maintaining the system in balance.
When condensate evaporates from the discharge leg, and an equivalent volume of condensate is not collected within the housing, the lost volume is not replaced. The elevation of the fluid interface in the collection leg will be lowered. Addition of lubricant based on fill port levels, dipstick measurements, or sight glass levels will only further lower the lubricant-water interface in the collection leg. Continued unbalanced evaporation of condensate from the discharge leg can cause a transfer of the lubricant from the collection leg to the discharge leg. The lubricant or primary fluid will migrate to the top of any condensate remaining in the discharge leg. This results in lubricant discharge from an otherwise functional system, thus upsetting the balance of the system further.
The lubricant that is drained into the discharge leg is no longer available to the drive mechanism through the collection leg. If condensate forms within the drive housing it will migrate to the collection leg. The lubricant that has migrated to the discharge leg is then raised to the discharge port and discharged. When the primary and secondary fluid interface in the collection leg rises above its design elevation, gear teeth, bearings or other components are potentially exposed to the condensate, and the volume of the lubricant present to lubricate components or to act as a seal is reduced resulting in decreased drive system reliability.